This synthetic image is represented in three-dimensional projections so as to best correspond to the reality of the outside landscape.
This image generally includes piloting and navigation information known by the acronym “PFD”, meaning “Primary Flight Display”. Such information comprises, in particular, a scale representative of the pitch of the aircraft known by the term “pitch scale” as well as a symbol representative of the direction of the aircraft known by the acronym “FPV”, meaning “Flight Path Vector”. The image is generally displayed on the display screens of the aircraft instrument panel. FIG. 1 schematically represents this type of display in which there are a dotted-line representation of the outside landscape T, a pitch scale PE represented by graduations and a symbol A of the FPV.
The graphic representation of information superimposed on the representation of the outside landscape poses a certain number of problems.
The first problem is that the perfect three-dimensional projection of a landscape is not necessarily perceived as such by the pilot. To counter this difficulty, the patent U.S. Pat. No. 8,159,416 entitled “Synthetic vision dynamic field of view” describes a dynamic change of the field of view, or “FOV”, the acronym “Field Of View”, to have a better knowledge of the situation as a function of the speed of the aeroplane or of its altitude. For example, the FOV increases when the aeroplane is on the ground such that the pilot can see more widely to the sides and the FOV decreases at altitude. This system therefore allows the field of view to be zoomed without deformations. This solution only imperfectly resolves the absence of realistic aspect of the outside landscape or perceived as such.
A second problem is the display of the piloting information and, in particular, of the pitch scale when it has to be superimposed on the synthetic image of the outside landscape. In the absence of SVS representation, the pitch scale, which consists of graduations, is generally linear, that is to say that the spacings of its graduations are constant.
In an SVS representation, this linear representation can no longer conform, that is to say be perfectly superimposed on the landscape represented on the screen. Indeed, the principles of graphic generation of a three-dimensional or 3D image on a screen involves a projection of the 3D image in a two-dimensional plane. The result thereof is a deformation of the 3D scene displayed on the screen according to a law proportional to the tangent function. According to this principle, a three-dimensional object representing a linear scale becomes a nonlinear scale once projected into a plane. One way to resolve the problem is to modify the pitch scale by the application of the projection function, proportional to the tangent function. The patents U.S. Pat. No. 8,344,911 entitled “System, module, and method for generating non-linearly spaced graduations for a symbolic linear scale” and U.S. Pat. No. 7,825,831 “Aircraft flight display with a non-linear pitch scale” describe solutions of this type. These presentation methods do not make it possible to ensure both a satisfactory synthetic image presentation and an undistorted superimposition of the pitch scale.